The use of laminating compositions comprising an unsaturated polyester polymer, an ethylenically unsaturated curing agent reactive with the polyester polymer for curing the composition and a catalyst for the cure reaction to form laminated resinous articles is well known. A plurality of thin layers of the liquid composition are successively superimposed over a die or mold, typically with at least partial cure of each layer before superimposition of the next, to build up the laminated article. Usually the article will be reinforced by incorporating a reinforcing filler such as glass fiber, and this may be either applied separately as a mat or fabric of long glass fibers which is impregnated with the liquid composition to form some or all of the layers or it may be predispersed as short strands in the liquid composition. Of the many kinds of articles that can be made in this way, among the most important are boats, automotive body parts, and plumbing fixtures such as tubs and shower enclosures.
The cure of unsaturated polyester laminating compositions is commonly catalyzed by free radial catalysts such as suitable peroxides. The cure can be additionally accelerated, especially at ambient temperature, by the further inclusion of promoters such as cobalt salts and/or tertiary amines. Such catalyst promoters are ordinarily incorporated into the liquid formulation during its compounding well in advance of use and the catalyst subsequently added only immediately prior to use, for once the catalyst is present the compositions will quickly thicken and gel, and ultimately harden, to consistencies unusable for laminating and must therefor be used within a short time.
Where a large proportion, e.g. at least about 25 percent by weight based on the total weight of polyester polymer and curing agent, of non-reinforcing filler is incorporated in the laminating composition, it has been found advantageous to increase the proportion of promoter in order to overcome the cure retarding effect of such heavy filler loadings which is thought to arise from the filler acting as a heat sink to dampen the autocatalytic exothermic temperature rise which normally occurs during the cure reaction. Common non-reinforcing fillers used at high loadings are clays, calcium carbonate, hydrated alumina and the like. When included at about 75 to 100% loadings, the use of about 0.35% N,N-diethylaniline as promoter, all based on the total weight of polyester and curing agent, is typical. High loadings of such non-reinforcing fillers are ordinarily employed in fabricating plumbing fixtures, since they can contribute to meeting requirements for low smoke and flame spread.
When styrene-containing unsaturated polyester laminating compositions are disposed as thin layers during the laminating process, it has been found that objectionable evaporation of styrene therefrom can be reduced if small proportions of wax, such as paraffin wax, are included in and compositions. Only very small amounts of wax are required, from about 0.03 percent up to usually less than one percent by weight, based on the total weight of polyester and curing agent, to reduce the emission of styrene significantly.
However, the incorporation of even such small proportions of wax tends to interfere with the development of interlaminar adhesion in the cured laminated articles formed from these wax-containing compositions. The improved compositions and methods of the present invention provide an advantageous enhancement in the development of interlaminar adhesion while retaining the desiraable suppression of styrene evaporation in wax-containing liquid unsaturated polyester laminating compositions not heavily loaded with non-reinforcing filler.